The present invention relates to neuroprosthetic devices, and more particularly, to a surface neuroprosthetic device having an internal cushion interface system for improved functional electrical stimulation.
It is known that movement impairment in a limb can result from various neurological or orthopedic pathological conditions, such as stroke, spinal cord injury, head injury, cerebral palsy and multiple sclerosis. Selected muscles of the impaired limb can be triggered to contract and to perform a controlled functional activity, such as walking and standing or grasping and lifting, by surface Functional Electrical Stimulation (FES). FES has been used both as a therapeutic modality and for the improvement or restoration of impaired activities.
Devices based on FES have been developed for activating specific body sites. Such devices for the lower limb include gait restoration and gait modification systems, such as the dropfoot system for activating the ankle joint, and systems that, in addition, activate the knee joint. Typical examples of devices for stimulating the lower limb are U.S. Pat. No. 4,697,808 to Larson, et al., and Liberson, et al., Arch. Phys. Med. and Rehabilitation, pp. 101-105 (February 1961). Other devices for the upper limb, such as U.S. Pat. No. 5,330,516 to Nathan, activate the hand, wrist, or elbow.
U.S. Pat. No. 5,330,516 teaches that to relieve regions of high localized pressure between a splint and a hand, semi-rigid padded plates may be inserted between the splint and the skin. This is particularly applicable to the dorsal surface of the hand, where splint/skin contact pressures are high during hand prehension. It must be emphasized that the purpose and function of these pads is to provide comfort, and not serve to support the electrodes, nor to promote the conforming of the electrode contact surface to the skin.
Additionally, there is a danger in known rigid and semi-rigid devices of pinching soft body-tissue between the shells while closing the device. This is particularly dangerous where sensory touch and pain feedback are impaired in various neurological pathologies.
U.S. Pat. No. 5,695,452 to Grim, et al., and U.S. Pat. No. 6,179,800B1 to Torrens are typical examples of a device imposing foam or padding between a shell surrounding a limb. Neither device is a FES device, nor do the devices include electrodes. U.S. Pat. No. 6,179,800B1 discloses a method of reduction of Colles"" fracture, a specific type of wrist fracture. A splint includes first and second collars pivotally supported on a limb and adjustable to adjust the internal dimensions of the splint. The splint is provided with a support for supporting the extremity of the limb. Although the support allows some movement of the limb extremity, it is appreciated that the device is directed towards immobilization of the limb. By sharp contrast, neuroprosthetic devices require limb and muscle mobility, along with proper positioning of the electrodes against the contour of the skin surface, and maintaining sufficient and even electrode contact pressure as the contour changes with the contraction and relaxation of the stimulated muscles.
During activation of a limb or body site by a surface neuroprosthesis, the stimulation current flows through the electrode, through the skin and interposing biological tissues to the motor nerve, thereby activating the muscle. The effectiveness and comfort of a neuroprosthesis electrode is a complex issue, but is strongly influenced by the mechanical nature of the electrode-skin contact, as well other factors such as the electrical impedances of the electrode and skin component layers, the presence of any conductive liquid interposed between the electrode and skin, and the proximity to the stimulation site of target excitable tissue, and of afferent skin sensors.
The mechanical requirement at the electrode-skin interface is ideally an evenly-distributed pressure of sufficient magnitude depending on the magnitude of the current density being transmitted across the interface. Uneven pressure distribution can result in poor conduction of the stimulation current over a portion of the electrode and reduction in activation of excitable tissue under this electrode portion, together with an increase in the stimulation current density over other portions of the electrode. A high local concentration of the stimulation current density applied to the skin is referred to as a xe2x80x9chot spotxe2x80x9d and is to be avoided in view of the discomfort or pain associated with passing such high intensity stimulation currents through the afferent skin sensors.
The result of uneven electrodexe2x80x94skin contact pressure will thus be unreliable and uncomfortable activation of the body limb.
U.S. Pat. No. 4,182,320 to Sweeney and U.S. Pat. No. 5,507,836 to Pohlig disclose inflatable or fluid-pressurized sleeves. U.S. Pat. No. 4,182,320 teaches a disposable, foldable and inflatable protective sleeve for a conventional, re-usable, rigid splint board. The sleeve is not a FES device.
U.S. Pat. No. 5,643,332 to Stein, and U.S. Pat. No. 4,580,563 to Petrofsky disclose FES devices. Neither device has a rigid or semi-rigid exoskeleton shell. U.S. Pat. No. 5,643,332 uses a flexible band, while U.S. Pat. No. 4,580,563 uses a cuff having a zipper for securing the cuff to a arm, thereby assuring that the electrodes are secured at place.
In understanding the requirements of the above-cited art, it must be emphasized that the neuroprosthesis requires the application of sufficient pressure to the regions of the electrodes. A sleeve, by definition, essentially encircles the body limb; such that elastic, pneumatic, or hydraulic pressure applied by the sleeve to the limb tends to compress substantially the whole limb circumference. The application of the requisite electrode contact pressure to the whole limb circumference can result in various deleterious effects such as discomfort, where the neuroprosthesis is in use for long periods, and impairment in the flow of biological fluids through the soft tissue of the limb. Reduction of the radial pressure exerted by the sleeve to allow unimpeded blood flow may result in insufficient electrode pressure, and consequently, partial loss of electrode contact.
A further barrier in the use of a soft elastic sleeve and the like is the requirement for the hemiplegic patient having one plegic hand to don and doff the device. Because the soft elastic sleeve lacks structural rigidity, the patient is faced with mechanical problems, often insurmountable, in positioning the sleeve accurately and in fastening it securely on the limb using only one hand.
Thus, there is a recognized need for, and it would be highly advantageous to have, an internal cushion system for semi-rigid exoskeleton-type neuroprosthetic devices that, in addition to providing comfort, is convenient to don and doff, enables adaptive positioning of the electrodes, and provides both the requisite pressure at the electrodexe2x80x94skin interface and flexibility so as to substantially conform the electrode to the changing shape of the limb.
The present invention is a surface neuroprosthetic device having an internal cushion system. According to one aspect of the present invention, there is provided a surface neuroprosthetic device for functional electrical stimulation (FES) having an internal cushion interface system, the device including: (a) an at least semi-rigid exoskeleton shell for covering at least a portion of a limb; (b) at least one cushion interface disposed between the shell and the limb, the cushion interface being directly attached to the shell, and (c) at least one electrical stimulation electrode associated with, and supported by, the cushion interface, wherein the cushion interface is configured to transfer pressure from the shell to the electrode, so as to provide electrical contact between the electrode and a skin surface of the limb, thereby effecting functional electrical stimulation of at least one muscle of the limb.
According to further features in the described preferred embodiments, the cushion interface and local body tissue underlying the skin surface have a substantially similar modulus of elasticity.
According to still further features in the described preferred embodiments, the cushion interface is designed to conform to the skin surface during contraction and relaxation of muscles of the limb.
According to still further features in the described preferred embodiments, the cushion interface is designed to conform to the skin surface during articulations of the limb.
According to still further features in the described preferred embodiments, the cushion interface is configured to distribute interactive forces between the cushion interface and the skin surface, so as to maintain an essentially natural contour of the limb.
According to still further features in the described preferred embodiments, the cushion interface is designed to transfer pressure from the shell to the electrodes, such that an even pressure is applied to the skin surface, maintaining thereby operative contact between the electrodes and the surface.
According to still further features in the described preferred embodiments, the modulus of elasticity of the cushion interface is obtained using a solid filler material.
According to still further features in the described preferred embodiments, the cushion interface includes a compartment pressurized by a hydraulic fluid.
According to still further features in the described preferred embodiments, the cushion interface includes a compartment pressurized by air.
According to still further features in the described preferred embodiments, the exoskeleton shell is a rigid exoskeleton shell.
According to still further features in the described preferred embodiments, the exoskeleton shell is further designed and configured to be donned using a single hand.
According to still further features in the described preferred embodiments, the cushion interface includes an adaptive mechanical cushion.
According to still further features in the described preferred embodiments, the adaptive mechanical cushion has a substantially negligible damping constant.
According to still further features in the described preferred embodiments, the adaptive mechanical cushion has a damping constant sufficiently low such that the electrode maintains dynamic contact with the surface during contraction and relaxation of muscles of the limb.
According to still further features in the described preferred embodiments, the device further includes adjusting means for attaching the adaptive mechanical cushion to the shell, so as to allow adjusting a distance between the adaptive mechanical cushion and the shell, permitting, thereby, continuous and effective contact between the electrode and the surface.
According to still further features in the described preferred embodiments, the device further includes a mechanism for opening and closing of the neuroprosthetic device, wherein the mechanism is configured to transfer pressure from the shell to the cushion so as to avoid pinching of a soft tissue of the limb as the device is donned and doffed.
According to still further features in the described preferred embodiments, the mechanism is a linear closure mechanism.
According to still further features in the described preferred embodiments, the adaptive mechanical cushion includes at least one mechanical spring, associated with the shell, for providing a pre-determined effective modulus of elasticity.
According to still further features in the described preferred embodiments, the device further includes a mechanism for reversible opening and closing of the neuroprosthetic device, the mechanism being configured to transfer pressure from the shell to the adaptive mechanical cushion so as to avoid pinching of a soft tissue of the limb.
According to still further features in the described preferred embodiments, the device further includes elastic straps operatively connected to the shell, and wherein the electrode is connected to the straps, such that closing of the mechanism tensions the elastic straps so as to press the electrode to the surface of the limb.
According to still further features in the described preferred embodiments, the surface of the cushion interface system is affixed to the exoskeleton shell, the surface of the cushion system having a substantially arc-like cross-section to interface with a body limb.
According to still further features in the described preferred embodiments, the cushion interface is associated with the shell solely in regions of the surface of the cushion where electrodes are positioned.
According to another aspect of the present invention, there is provided a method of donning a neuroprosthetic device for functional electrical stimulation (FES), the device having an internal cushion interface system, the method including the steps of: (a) providing a surface neuroprosthetic device having: (i) an at least semi-rigid exoskeleton shell for covering at least a portion of a limb; (ii) at least one cushion interface disposed between the shell and the limb, the cushion interface being directly attached to the shell, and (iii) at least one electrical stimulation electrode associated with, and supported by, the cushion interface, (b) covering the portion of the limb with the neuroprosthetic device so as to transfer pressure from the exoskeleton shell to the electrode, thereby providing electrical contact between the electrode and a skin surface of the limb, so as to effect functional electrical stimulation of at least one muscle of the limb.
According to further features in the described preferred embodiments, step (b) of the method is performed with a single hand.